With respect to the front end of a motor vehicle, as is well known, in the engine compartment the body has at least two longitudinal struts, which protrude forward from the passenger compartment at a height substantially equal to that of the front wheel arches, and at their front points support a front end of the vehicle.
This front end comprises a cross-member connected to the struts by means of two buffering elements, which are defined by box elements, generally made of metallic material, which deform plastically to absorb energy in the event of impacts at moderate speed (less than 16 km/h) and are generally known as the “crash-box”.
Each strut is equipped with an attachment plate attached, for example by means of bolts, to a supporting plate which in turn is attached to the rear end of the corresponding box buffering element. The attachment plate is fitted around the front point of the strut and has one or more tabs welded to this point. The attachment plate also has a front wall which is substantially vertical and is radiused to such tabs and rests against the support plate of the corresponding buffering element, at a resting plane.
In general, the front edge of each strut is longitudinally spaced, for example by 2-7 mm, from the resting plane of the plates. This value can be different for different vehicles and between the two struts of each vehicle and is specially adjusted by varying the longitudinal position where the two attachment plates are welded, in order to correct tolerances for machining and coupling of the parts of the body that were previously assembled and in order to obtain a perfect orthogonality between the resting plane of the plates and the longitudinal axis of advancement of the vehicle.
In the known solutions, the tabs of the two attachment plates protrude rearwards and terminate longitudinally with respective edges that are welded to the outer lateral surfaces of the struts by means of welding seams.
Solutions of this type are not entirely satisfactory as regards the distribution of the loads on the two attachment plates and the consequent behaviour of the buffering elements during plastic deformation in the event of a frontal impact of the motor vehicle.
In fact, the load due to the collision is transmitted by each buffering element to the corresponding strut at the resting zone between the two plates. This resting zone is annular and is spaced outwardly from the fastening points of the two attachment plates, defined by their tabs and by the aforesaid welding seams. This radial distance defines a lever arm which generates a high bending moment on the front walls of the two attachment plates. Therefore, they tend to bend excessively during impact. An excessive flexural deformation of the mounting plates is undesirable, since it tends to make the actual behaviour of the buffering elements become unstable and therefore unpredictable during their plastic deformation.
Given this uncertainty, the amount of energy actually absorbed by the buffering elements could be less than the projected amount calculated. Therefore, in practice, it is necessary to over-size the buffering elements and also the other elements of the front structure of the body, with a consequent increase in weight.